Abrading apparatus

ABSTRACT

Apparatus for abrasively trimming resistors and other electrical elements is provided with means for manually interrupting the trim cycle in order to trim more precisely. Control components, including a solenoid valve and a gang switch operate to divert pressurized air from the air motor of the traversing mechanism and to stop the abrasive stream when the switch button is depressed. Trimming resumes when the switch button is released. Repeated depression of the switch button during the trim cycle enables the operator to trim precisely. A foot switch is also depressed until the end of the trim cycle.

nied States Patent Callahan et al. Nov. 5, 1974 [5 ABRADING APPARATUS3,778,935 12/1973 Callahan 51/8 [75] Inventors: John William Callahan,Lanoka Harbor, Martin John Primary ExaminerDonald G. Kelly Capdevme,Staten Island, Attorney, Agent, or FirmEdward A. Sager 73 Assi nee:Pennwalt Cor oration Philad l h 1 g Pa. p ep 7] ABSTRACT [22] Filed. May15 1973 Apparatus for abrasivcly trimming resistors and other electricalelements is provided with means for manul PP ,496 ally interrupting thetrim cycle in order to trim more precisely. Control components,including a solenoid [52] us Cl 51/12 valve and a gang switch operate todivert pressurized [51] 3/32 air from the air motor of the traversingmechanism [58] Field 5 12 l 4 and to stop the abrasive stream when theswitch button is depressed. Trimming resumes when the switch [56]References Cited button is released. Repeated depression of the switchbutton during the trim cycle enables the operator to UNITED STATESPATENTS trim precisely. A foot switch is also depressed until the3,534,503 10/1970 Kulischenko 51/8 end f the trim Cycle, 3,593,4597/197l Kulischenko 4 5l/8 3,691,695 9/1972 Green 51/8 9 Claims, 1Drawing Figure ABRADING APPARATUS SUMMARY OF THE INVENTION Thisinvention relates to abrading apparatus, more particularly to apparatusfor trimming electrical components such as resistors to the desiredelectrical value with a jet of airborne abrasive powder or particles.

The basic abrading apparatus comprises an air supply, a powder reservoirwith vibrator and mixing chamber, and a supply conduit fitted with anappropriate nozzle, Under pulsation from the vibrator abrasive powdertrickles into the pressurized airstream, the amount depending on theamplitude of vibration. A rheostat may be employed to regulate theamplitude of vibration and, consequently, the intensity of abrasivecutting action.

To the basic abrading apparatus is added a control system, also acontrolled drive with stop-action for the nozzles. It is contemplatedthat a work-piece such as a resistor will be placed ina holder.Thereafter, on signal the machine starts the abrasive jet flow andnozzle mo- I tion, and stops the entire proceedings when predeterminedresistance values have been reached.

According to the present invention, provision is made to permit theoperator of an abrasive trimming device to interrupt the trimmingoperation optionally without returning the nozzle to the originalstarting position. This is accomplished by depressing a push buttonwhile keeping a foot switch depressed. By repeatedly depressing the pushbutton the operator can effect incremental advances of the traversingmechanism until the final desired value of the component being trimmedis achieved.

A foot switch is depressed to initiate the trim cycle, and it is held indepressed position while the push button is used to make incrementaladvances. When the foot switch is released the trim cycle is terminatedand the apparatus returns to starting position.

By addition of a three-way solenoid valve to the supply line forpressurized air, the abrading unit may be stopped during suchinterruption and both'sides of a double acting piston in the air motorare then vented to atmosphere. This action stops the traversingmechanism. Upon deenergizing the three-way solenoid valve the air motoris repressurized and traversing may continue without returning to startposition. At any time during the trim cycle, whether or not the trimmingoperation is being interrupted, the operation may be terminated and thenozzle returned to start position by removing pressure from the footswitch.

DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is adiagramatic view of abrading apparatus embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The illustratedabradingapparatus will now be described as to the trimming of athick-film resistor, elecfrom a compressor 18 is uniformly mixed in thedesired proportions with abrasive powder from a reservoir 20.

By means of an arrangement more fully described in US. Pat. No.3,344,524, a vibrator 22 is employed to apply vibrations to the chamber16. This arrangement can produce a trickle of about 3 to 5 grams perminute of aluminum oxide or other abrasive powder having an averageparticle size of 27 microns, from the reservoir 20 through a passageway(not shown) to the mixing chamber 16 for combining with pressurized air.

The flow of airborne abrasive particles is initiated by the energizationof a solenoid operated valve 24 in the upstream end of the supply tube14, that is, at the outlet of the mixing chamber 16. The nozzle 12 willhave a restricted orifice, e.g. 0.0l8 inch diameter, of much smallercross-sectional flow area than the supply tube 14. In order to achieveuniform cutting action the apparatus isarranged to provide a uniformconcentration of particles in a constant airstream issuing from thenozzle at about 40 to psi.

Valve 24 may be a solenoid operated pinch valve. The supply tube14 maybe a flexible hose of abrasion resistant material at the end of a lengthof rigid tubing, and it is preferred that the terminal or end portionadjacent the nozzle 12 be of rigid tubular construction so that it canserve as nozzle holder 26 capable of having its movements accuratelycontrolled by a traversing mechanism 28 connected thereto by a rigidlyconstructed arm 30. The nozzle holder 26 is suitably journaled in theextended free end of the arm 30, in upright position above a holder 32for the workpiece 10. Further details of construction of the traversingmechanism 28 appear herein and it is noted here that the mechanism 28serves to move the nozzle 12 by its holder 26 transverse to thelongitudinal extent of the holder, whereby the abrasive stream istraversed along the length of the workpiece to cut or abrade along theline of travel.

The traversing mechanism 28 responds to controlled flow of pressurizedair through conduits 34 and 3S, commanded by a control 36, to move acontrolled distance first in one direction and then in opposite orreverse direction upon completion of an abrading operation. The control36 also sends energizing current through conductors 38 to the solenoidof valve 24 to effect its closing upon completion of an abradingoperation; but otherwise during abrasive trimming the valve 24 is heldopen.

The workpiece 10 may be an electrical resistor having a thick,electrically resistive film printed on a correspondingly shapedsubstrate, as more fully described in US. Pat. No. 3,589,081.

The traversing mechanism 28 is shown as an air motor having a cylinder40 containing a double acting piston 42 secured to the arm 30. The innerend of the arm 30 acts as a piston rod and carries thereon pistons 44and 46 of a variable hydraulicdamper system.

Hydraulic fluid is contained in the damper system, including chambers 48and 50 within the cylinder, as well as loop line 52 and bypass line 54.As the arm 30 moves leftward, fluid in chamber 48 is displaced clockwisethrough bypass line 54 to chamber 50 at a rate permitted bya flowregulating valve 56 in bypass line 54. Fluid is prevented from flowingclockwise through loop line 52 by check valve 58. However, when the arm30 moves rightward and creates a region of reduced pressure in chamber48 fluid returns thereto via loop line 52. By this arrangement the speedof nozzle 12 travel during trimming of a workpiece I0 is regulated bythe damper system in accordance with the setting of valve 56.

The arm 30 is driven leftward when pressurized air is introduced viaconduit 35 to chamber 60, while chamber 62 is simultaneously vented toatmosphere via conduit 34. The pressure differential on opposite sidesor faces of piston 42 effects movement in the direction of the side oflower pressure. Accordingly, the arm 30 is reversed or moved rightwardby venting chamber 60 to atmosphere through conduit 35 whilepressurizing chamber 62 through conduit 34.

Pressurization and venting of the chambers 60 and 62 is effected by afour-way solenoid valve 64. in the deenergized position, as shown,solenoid valve 64 connects conduit 34 to a supply line 66 forpressurized air. Line 66 is connected through a main air supply line 68to the air compressor 18. Also while deenergized, solenoid valve 64connects conduit 35 to atomsphere through a vent tube 70. When solenoidvalve 64 is energized the connections are reversed; and conduit 35 isconnected to supply line 66, while conduit 34 is connected through venttube 70 to atmosphere.

Main air supply line 68 feeds pressurized air in parallel to supply tube14 and supply line 66 from compressor 18 so long as solenoid valve 72 inline 68 is energized. Solenoid valve 72 is normally closed, but it openswhen energized directly from main electrical conductors L1 and L2 uponclosing main switch 74.

Closing main switch 74 also connects foot switch 76 to L1. in normalposition, as shown, foot switch is held by a spring force with its bladeagainst contact 78, thereby energizing solenoid valve 24 throughconductors 38 and closing supply tube 14 to flow of any abrasive stream.It is to be noted that in the illustrated position of foot switch 76 thevibrator 22 and the solenoid valve 64 are deenergized. Therefore, whenthe main switch 74 is closed and the foot switch 76 is not yetdepressed, the delivery of air to mechanism 28 retracts the arm 30 andnozzle 12 rightward and holds them in this starting and ending positionof a trim cycle.

Depressing foot switch 76 brings its blade into engagement with contact80 after disengagement with contact 78. With switch 74 closed thisaction deenergizes solenoid valve 24 and opens tube 14 to flow, whileenergizing solenoid valve 64 through conductor 82 to initiate leftwardmotion of the nozzle 12. At the same time vibrator 22 is energizedthrough the normally closed contacts 84 of gang switch 86. Thus,depressing foot switch 76 initiates the trimming operation and with theillustrated apparatus trimming may continue until pressure on the footswitch is released.

Various well known automatic control devices are available forinterrupting a trim cycle. These may be used with the apparatusdescribed herein. but a description thereof is omitted for the sake ofbrevity.

Gang switch 86 includes normally open contacts 88 between L1 andconductors 38 to solenoid 24, also normally open contacts 90 betweencontact 80 of foot switch 76 and three-way solenoid valve 92 in conduit35. Gang switch 86 is a push button switch held positioned as shown by aspring or other suitable biasing force. When switch 86 is depressed itsblades will bridge and close contacts 88, also contacts 90 respectively;and another blade will disengage contacts 84.

Gang switch 86, together with solenoid valve 92, provides a convenientmeans for manually interrupting and continuing the trimming cycle whilethe foot switch 76 is depressed, its blade engaging contact 80. Bypushing and releasing the push button of gang switch 86 it is possibleto effect very small incremental movements of the nozzle. Flow of theabrasive stream is interrupted while the traversing mechanism 28 ishalted; and flow resumes when traversing movement continues. With thisarrangement more precise manual trimming is possible.

When solenoid valve 92 is deenergized, conduit 35 is open for flow ineither direction, and it is closed to a vent 94 leading to atmosphere.Thus, with foot switch 76 not depressed, chamber 60 is vented toatmosphere through conduit 35, deenergized valves 92 and 64, and ventand, with foot switch 76 depressed, chamber 60 is pressurized from line66 through energized solenoid valve 64, deenergized solenoid valve 92,and conduit 35.

Solenoid valve 92 can only be energized through the contacts of gangswitch 86 when the foot switch 76 is depressed and its blade engagescontact 80. When the circuit is thus conditioned a trim cycle is inprogress, with pressurized air flowing through conduit 35 toward chamber60. Upon pressing the push button, gang switch closes contacts 90 toenergize solenoid valve 92. As a result, conduit 35 is blocked andchamber 60 is vented to atmosphere through vent 94. With chamber 62 alsovented to atmosphere through valve 64 and vent 70, piston 42 isunpressurized and is at a standstill. Gang switch 86 simultaneouslyopens contacts 84 and deenergizes the vibrator 22, plus closes contacts88 to energize solenoid valve 24 and close the supply tube 14.

With the present invention provision is made for interrupting a trimcycle to effect precise trimming under manual control by the simple andinexpensive addition of three-way solenoid valve 92 and gange switch 86.

The invention may be applied to apparatus for trimming capacitors andother electrical elements, as well as for trimming resistors.

The solenoid valves 24, 64, 72 and 92 are shown in de-energizedposition, each with a tension spring which is stretched when itsassociated field coil is energized and which therefore biases the valveto de-energized position when it is in energized position.

We claim:

1. In apparatus for adjusting the electrical value of an electricalelement by abrasion, including a pressurized air supply, an abrasivepowder supply, a device connected to said air supply and said powdersupply for mixing pressurized air and abrasive powder to provide astream of airborne abrasive powder, a nozzle for directing said streamat an electrical element undergoing adjustment of its electrical value,a tube connecting said nozzle to said device for delivering said streamto said nozzle, a traversing mechanism including an air motor powered bypressurized air for moving said nozzle along said electrical elementfirst in one direction during adjustment of electrical value and then inreverse direction to start position after adjustment of electricalvalue, and a first control for controlling the flow of pressurized airto said air motor for effecting movement of said nozzle in one directionand in reverse direction, that improvement comprising a second controlfor interrupting the flow of pressurized air to said air motor duringmovement of said nozzle in one direction.

2. Apparatus as described in claim 1 wherein said first control andsecond control are electrically operated solenoid valves.

3. Apparatus as described in claim 2 wherein said first control includesmeans, operable when said first control is actuated, for effectingmovement of said nozzle in one direction and for simultaneouslyconditioning said second control for operation, and wherein said firstcontrol further includes means for effecting movement of said nozzle inreverse direction and for simultaneously deconditioning said secondcontrol for operation when said first control is deactuated.

4. Apparatus as described in claim 2 wherein said first control is afour-way solenoid valve which in first position connects said air motorto said air supply and to atmosphere for moving said nozzle in onedirection, and which in second position reverses the connection of saidair motor in first position to said air supply and to atmosphere formoving said nozzle in reverse direction.

5. Apparatus as described in claim 4 wherein said second control is athree-way solenoid valve which when energized with said first control infirst position blocks the flow of pressurized air to said air motor fromsaid air supply and vents the connection of said air motor to said airsupply established in first position of said first control, whereby saidair motor is halted without moving said nozzle in reverse direction.

6. Apparatus as described in claim 5 wherein said second controlincludes means operable in deenergized position of said second controlfor conducting the flow of pressurized air between said air motor andsaid first control in the first position of said first control andoperable for conducting air vented from said air motor to atmosphere insecond position of said first control.

7. Apparatus as described in claim 2 wherein said device is electricallyoperated, further including a push button gang switch which in firstposition dcenergizcs said device and energizes said second control. andwhich in second position energizes said device and deenergizes saidsecond control, said gang switch including means biasing it to firstposition.

8. Apparatus as described in claim 7 having a third control comprising asolenoid valve in said tube which is normally open in deenergizedposition thereof, said gang switch in first position energizing saidthird control to close said tube and in second position deenergizingsaid third control to open said tube.

9. Apparatus as described in claim 1, said air motor comprising acylinder, a double acting piston movable in said cylinder and connectedto said nozzle for reciprocating movement therewith in said onedirection and reverse direction, said piston being driven in said onedirection by introducing pressurized air to said cylinder on one side ofsaid piston and by venting the other side of said piston.

1. In apparatus for adjusting the electrical value of an electricalelement by abrasion, including a pressurized air supply, an abrasivepowder supply, a device connected to said air supply and said powdersupply for mixing pressurized air and abrasive powder to provide astream of airborne abrasive powder, a nozzle for directing said streamat an electrical element undergoing adjustment of its electrical value,a tube connecting said nozzle to said device for delivering said streamto said nozzle, a traversing mechanism including an air motor powered bypressurized air for moving said nozzle along said electrical elementfirst in one direction during adjustment of electrical value and then inreverse direction to start position after adjustment of electricalvalue, and a first control for controlling the flow of pressurized airto said air motor for effecting movement of said nozzle in one directionand in reverse direction, that improvement comprising a second controlfor interrupting the flow of pressurized air to said air motor duringmovement of said nozzle in one direction.
 2. Apparatus as described inclaim 1 wherein said first control and second control are electricallyoperated solenoid valves.
 3. Apparatus as described in claim 2 whereinsaid first control includes means, operable when said first control isactuated, for effecting movement of said nozzle in one direction and forsimultaneously conditioning said second control for operation, andwherein said first control further includes means for effecting movementof said nozzle in reverse direction and for simultaneouslydeconditioning said second control for operation when said first controlis deactuated.
 4. Apparatus as described in claim 2 wherein said firstcontrol is a four-way solenoid valve which in first position connectssaid air motor to said air supply and to atmosphere for moving saidnozzle in one direction, and which in second position reverses theconnection of said air motor in first position to said air supply and toatmosphere for moving said nozzle in reverse direction.
 5. Apparatus asdescribed in claim 4 wherein said second control is a three-way solenoidvalve which when energized with said first control in first positionblocks the flow of pressurized air to said air motor from said airsupply and vents the connection of said air motor to said air supplyestablished in first position of said first control, whereby said airmotor is halted without moving Said nozzle in reverse direction. 6.Apparatus as described in claim 5 wherein said second control includesmeans operable in deenergized position of said second control forconducting the flow of pressurized air between said air motor and saidfirst control in the first position of said first control and operablefor conducting air vented from said air motor to atmosphere in secondposition of said first control.
 7. Apparatus as described in claim 2wherein said device is electrically operated, further including a pushbutton gang switch which in first position deenergizes said device andenergizes said second control, and which in second position energizessaid device and deenergizes said second control, said gang switchincluding means biasing it to first position.
 8. Apparatus as describedin claim 7 having a third control comprising a solenoid valve in saidtube which is normally open in deenergized position thereof, said gangswitch in first position energizing said third control to close saidtube and in second position deenergizing said third control to open saidtube.
 9. Apparatus as described in claim 1, said air motor comprising acylinder, a double acting piston movable in said cylinder and connectedto said nozzle for reciprocating movement therewith in said onedirection and reverse direction, said piston being driven in said onedirection by introducing pressurized air to said cylinder on one side ofsaid piston and by venting the other side of said piston.